1. Field of the Invention
The present invention relates to a rotary transformer of disc type for use in an electromechanical apparatus such as video tape recorder or digital audio tape recorder for exchanging signal with respect to a rotary magnetic head of the electromechanical apparatus.
2. Description of Prior Art
A rotary transformer of this kind includes a stator and rotor cores of ferrite and coaxial coils fitted in coaxial grooves formed in facing surcaes of the respective ferrite core and various arts of forming and fitting such coaxial coils have been proposed. Typical examples of these arts will be described.
In a first conventional art, which is proposed in Japanese Patent Application Laid-open No. Hei 3-227003, a coil pattern including conductive coils and short-rings formed is on a base film adhered to a surface of a transformer core and, peeling the base film off, the coil pattern is transferred to the transformer core.
In a second conventional art proposed in Japanese Patent Application Laid-open No. Hei 1-130509 and particularly shown in FIG. 2 thereof, a composte coil member having conductive coils and short-rings is formed on a backing of a flexible sheet of insulating material, which has connecting portions for connecting and supporting the conductive coils and short-rings, is fitted in grooves formed in respective transformer cores.
In a third conventional art disclosed in Japanese Patent Application Laid-open No. Hei 2-308505, a plurality of composite coil members each including conductive coils are formed on a high molecular sheet by photolithography and the composite coil member composed of this sheet and the conductive coils is fitted in grooves formed in a transformer core while punching out the composite coil member from the sheet.
In a fourth conventional art disclosed in Japanese Patent Application Laid-open No. Sho 62-271406 and particularly shown in FIGS. 2 and 3 thereof, a composite coil member composed of conductive coil patterns formed on both surfaces of an insulating layer and electrically connected to each other through through-holes formed in the insulating layer is fitted in coaxial grooves formed in a transformer core.
In a rotary transformer including a composite coil member for signal transmission, which is composed of a flexible support member of insulating material and coils formed thereon by using photolithigraphy, and transformer cores each having grooves in which the composite coil member is fitted, the following points are important in views of assembling of the rotary transformer and performance thereof:
(a) Good pressure contact of the composite coil member to the grooves of the transformer core. PA1 (b) No need of peeling the coil support member after the composite coil member is fitted in the grooves. PA1 (c) Easiness of holding the coaxial conductive coils without deformation before fitting them in the grooves. PA1 (d) Easiness of forming the coils and the coil support member having configuration met the groove configuration of the core. PA1 (e) A desired number of turns of the conductive coil is obtainable within a limited area.
In the first conventional art mentioned above, the conductive coils formed on the base film are adhered to the transformer core and then transferred thereto by peeling the base film off. In transferring the coils, it is necessary to apply pressure thereto from the side of the base film. Therefore, there are problems, in transferring the coils to the grooves of the transformer core, that the coils can not received in the grooves of the core correctly due to rigidity of the base film and that the base film must be peeled off after the transfer.
In the second conventional art mentioned above, the connecting portions extend along the diameter direction and support each of the coaxial coils at two locations and the composite coil member is fitted in the grooves of the transformer core together with their the backing of the coaxial flexible insulating member. Assuming that the coils are for a rotary transformer of multi-channel type, radially outer coils may not be supported enough by the connecting portions since portions of the outer coils which are not supported by the connecting portion become substantially long and, thus, it is very difficult to support the coils without deformation as a whole. Although it may be considered, in order to support the coils reliably or to make the coils correspondent to lead portions of coil terminals in case of multi-channel type, that the connection portion is made wider. In such case, however, a facing area of the transformer core is reduced correspondingly, resulting in degradation of performance of the rotary transformer.
In the third conventional art mentioned above, a sheet film on which the composite coil members are formed is positioned and held at a predetermined location by means of positioning holes formed along the sheet. The sheet is punched at that location to cut out the composite coil member from the sheet in alignment with the grooves of the transformer core, and, simultaneously therewith, the punched coil member is adhered into the grooves. In this case, however, corner portions of the composite coil member which connects the radially extending coil terminal portions and the coaxially arranged arc portions of the composite coil member are rounded due to structural limitation of a punching die. Therefore, it is necessary to preliminarily make each of the groove of the transformer core wider. Consequently, an area of the coil member facing the opposite transformer core is reduced correspondingly, resulting in degradation of performance of the rotary transformer. When such coil member is of a type which contributes to miniturization of a rotary transformer or is of multi-channel type, gap between adjacent coils is small and gap between adjacent grooves of the core is small necessarily. Therefore, tolerance of registration between the coils on the sheet film and the grooves of the core becomes small. Consequently, the structure of the punching die becomes complicated, mechanical strength of the punching die is degraded and/or manufacture of the punching die becomes difficult.
In the fourth conventional art, the composite coil member composed of the flexible insulating layer and the coils formed on the both surfaces of the insulating layer is fitted in the grooves of the transformer core. In this technique, when the coils on these surfaces have the same number of turns and are formed in substantially the same region when looked from either surface of the insulating layer, and when the region covers the width of the flexible insulating layer substantially, the coil patterns on the both surfaces of the insulating layer may be deviated from each other by a distance in the order of 0.1 mm, since these coil patterns must be formed by photo-lithography separately, and, therefore, portions of the coil patterns on edge portions of the insulating layer may be thinned or broken.